1. Field of the Invention
The present invention relates to an ultraviolet absorbing glass plate for use in buildings, vehicles, ships, airplanes and various display devices, and more particularly to a glass plate having an ultraviolet absorbing multilayer coating formed thereon.
2. Description of the Prior Art
Hitherto, various ultraviolet absorbing glasses have been proposed. For example, there is proposed a glass which is coated with an ZnO film for cutting ultraviolet rays.
JP-A-52-47812 discloses an ultraviolet absorbing colorless soda-lime glass which contains 0.15-1.2% CeO.sub.2, 0.002-0.12% V.sub.2 O.sub.5, 0.006-0.08% MnO.sub.2 or 0.004-0.04% Se, and not higher than 0.0004% Co.sub.3 O.sub.4 for providing the glass with the ultraviolet absorbing property.
JP-A-59-17925 discloses an agricultural deposition film comprising a plastic film and a synthetic resin film which contains an ultraviolet absorbing agent and is adhered to the plastic film.
The above-mentioned proposals (JP-A-52-47812 and JP-A-59-17925) are not suitable for a production method in which many types of products with small amounts are produced. Furthermore, the glass of JP '812 and the film of JP '925 tend to be colored or clouded if they are constructed so as to absorb ultraviolet rays having a wavelength of about 400 nm (the upper limit of the ultraviolet region).
JP-A-56-32352 discloses a heat reflecting laminated glass in which at least one of two polyvinyl butyral interlayer films contains an ultraviolet absorbing agent. This glass is improved in chemical resistance, abrasion resistance and durability, and does not tend to be colored or clouded because the ultraviolet absorbing agent is contained in the interlayer film. However, the glass tends to be too thick in thickness, and thus to be too heavy.
JP-A-4-76083 discloses an ultraviolet insulating film which comprises cerium oxide and a metal oxide of which metal has a valence larger than that of cerium.
JP-A-4-97103 discloses a method of producing an ultraviolet cutting filter. In this method, at first, water is added to a mixed solution containing an organic titanium compound, a cerium compound and a polyhydric alcohol so as to make a sol. Then, the sol is applied to a transparent substrate, and then the coated substrate is heated.
The above-mentioned proposals (JP-A-4-76083 and JP-A-4-97103) use inorganic compounds basically. Therefore, ultraviolet region which is closer to visible light region can not be sharply cut. Furthermore, it is necessary to bake at a temperature not lower than about 200.degree. C. Therefore, the proposals can not be applied to some glasses such as tempered glass.
JP-A-61-126503 discloses a method of producing an ultraviolet cutting synthetic resin plate by using a dispersion type fluorescent dye having a brightening effect such as 2,5 bis (5'-tertiary butyl benzo oxazolyl(2)) thiophene. This resin plate cuts ultraviolet rays and is superior in transparency without using an ultraviolet absorbing agent. However, fluorescence becomes too marked, and the resin plate is not good in durability.
Apart from the above-mentioned ultraviolet absorbing glass, there are some proposals of an infrared reflecting glass. For example, JP-A-63-239043 discloses an infrared reflecting glass which is coated with a five-layer coating comprising a first layer of ZnO film, a second layer of Ag film, a third layer of ZnO film, a fourth layer of Ag film and a fifth layer of ZnO film. The coated glass is not lower than 60% in the visible light transmittance.
JP-A-2-111644 discloses a laminated glass comprising first and second transparent glass plates and a conductive film formed on the first glass plate by the sputtering and an interlayer film which are interposed between the first and second glass plates. The conductive film is made up of five-layer, seven-layer or nine-layer film which is formed by alternately arranging ITO films as odd-numbered layers and Ag films as even-numbered layers.
The above-mentioned proposals (JP-A-63-239043 and JP-A-2-1116444) use a basic composition of a Ag film sandwiched between dielectric films. However, a Ag film deteriorates by water and a high humidity, thereby impairing infrared reflecting property. Therefore, it is necessary to interpose the infrared reflecting film between two glass plates.
Furthermore, there are some proposed ways to provide a glass with the infrared reflecting property together with the ultraviolet absorbing property. One example is a glass which contains ultraviolet absorbing compounds and coated with an infrared reflecting film. Another example is a laminated glass comprising transparent glass plates which are coated with an infrared reflecting film and interposes therebetween an interlayer film containing ultraviolet absorbing compounds. As still another example, JP-A-4-133004 discloses an ultraviolet and infrared cutting filter formed on a transparent substrate. The filter comprises a ZnO film formed on one side of the transparent substrate and a multilayer coating which is formed on the ZnO film and/or the other side of the transparent substrate. The multilayer coating is formed by alternately depositing transparent conductive oxidized films and transparent dielectric films having a high refractive index. The construction of the filter is very complicated for providing the ZnO film with humidity resistance and protection. Therefore, the production cost of the filter is high and durability of the same is not satisfactory.